Photographic flash exposure control system

ABSTRACT

A camera system comprises a flash device cooperative with a auto-flash mechanism in a camera. The flash device comprises a capacitor, a power supply circuit for charging the capacitor and a discharge lamp circuit including a discharge lamp. The flash device is further provided with a control circuit connected between the capacitor and the auto-flash mechanism for detecting the charge stored in the capacitor and providing output signal to control the auto-flash mechanism in the camera to obtain the optimum exposure.

United States Patent 11 1 Mashimo et a1.

PHOTOGRAPHIC FLASH EXPOSURE CONTROL SYSTEM Inventors: Yukio Mashimo,Meguro-ku, Tokyo;

Seiichiro Yokohama-shi,

Mizui, Naka-ku,

Kanagawa-ken;

Yoshiyuki Takishima, Kawasaki-shi, Kanagawa-ken, all of Japan Assignee:

Canon Kabushiki Kaisha, Tokyo,

Japan Filed:

April 13, 1970 Appl. No.: 27,699

Foreign Application Priority Data April 18, 19 69 June 20, 1969 June 20,1969 June 6, 1969 U.S. Cl.

Int. Cl.

Japan ..44/301l3 Japan.... ..44/4s735 Japan ..44/48736 Japan ..44/5305O.95/10 CE, 250/214 P, 315/241 P ..G03b 15/05, H05b 41/02 Field ofSearch..95/l0 C, 11 R, 11.5, .11 L,

95/10 CE; 250/214 P; 315/241 P 1 Feb. 6, 1973 [56] References CitedUNITED STATES PATENTS 2,901,671 8/1959 Most ..95/l 1.5 R X 2,946,924 7/1960 Gerlach et al...... ..3 15/241 P 3,350,604 10/ l 967 Erickson 315/241 3,424,071 l/1969 Schwahn .....95/1 115 3,438,766 4/1969 Biber..95/11 3,470,798 10/1969 Mikakawa ..95/l0 Primary Examiner-John M.Horan Assistant ExaminerFred L. Braun AttorneyAnton J. Wille [57]ABSTRACT A camera system comprises a flash device cooperative with aauto-flash mechanism in a camera. The flash device comprises acapacitor, a power supply circuit for charging the capacitor and adischarge lamp circuit including a discharge lamp. The flash device isfurther provided with a control circuit connected between the capacitorand the auto-flash mechanism for detecting the charge stored in thecapacitor and providing output signal to control the auto-flashmechanism in the camera to obtain the optimum exposure.

15 Claims, 11 Drawing Figures PATENTEDFEB s 1975 SHEET 10F 4 FIG.I

1 -2 L CS 9 RV fi 7 7 6 .wfi -v 3 MQT 4m w v 2 y m FIG. 2

PATENTED FEB 6 I975 SHEET 2 OF 4 FIG. 3

FIG.4

FIG. 5

PATENTED F B 5 I 7 SHEET Q 0F 4 value for flash exposure is known asdisclosed in U.S.

Patpltlo. 3,344,724. In one auto-flash mechanism as disclosed in U.S.Patent application Ser. No. 820,988, filed May 1, 1969, now U.S. Pat.No. 3,633,476, and U.S. Ser. No. 820,901, filed May 1, 1969, now U.S.Pat. No. 3,613,534, the focusing ring of a camera is cooperative with anaperture setting ring; a guide number of a flash device is set by anauto-flash switching ring on the side of the camera for setting theguide number; and a variable or adjustable resistor cooperative with thefocusing ring is connected to the electric eye'(EE) circuit in thecamera having a autoflash mechanism, thereby determining a stop value byan angle of deflection of a pointer of a meter. For flash exposure, theguide number of the flash device is generally considered constant when asuitable stop value or exposure factor is determined. When a flashdevice having no circuit for automatically maintaining constant avoltage charged across a main capacitor of the flash device,under-exposure tends to occur because of an insufficient charging of themain capaci- .tor.

An object of the present invention is to provide a flash device and acamera system having this flash device in which a voltage charged acrossa main capacitor of the flash device is detected by use of the autoflashmechanism of the camera and a meter such as an exposure meter of theautoflash-mechanism is so controlled as to automatically obtain theoptimum exposure.

According to one aspect of the present invention, an operator can viewthrough a viewfinder a signal representative of the completion of theflash device ready for flash exposure for example by the deflection ofthe pointer of a meter within the viewfinder.

According to another aspect of the present invention, theautoflash-mechanism is automatically controlled depending upon the powersource voltage or luminescence of the flash device so that even when thepower voltage is varied, it can be suitably compensated, therebyobtaining the optimum exposure all the time.

According to another aspect of the present invention, the variation involtage across the main capacitor of the flash device is indicated bythe deflection of the pointer of a meter, whereby flash exposure can beaccomplished at a desired stop value or aperture.

According to another aspect of the present inven-- tion, a control unitor circuit is interposed between the flash device and the auto-flashmechanism in such-a manner that a low voltage output is in proportion toa high power source voltage of the flash device, thereby matching one tothe other in a best manner.

'According to another aspect of the present invention, a flash devicehaving a control unit or circuit and a camera having a auto-flashmechanism are constructed as separate, independent units in such amanner that when the flash device is attached to the camera, flashexposure becomes possible by an extremely simple operation. Furthermore,it is very simple to switch between flash exposure and exposure withoutthe use of a flash bulb. When the flash device is detached from thecamera, exposure without use of the flash bulb may be obtained withoutspecial manipulations. Thus, it is seen that the camera construction isnot further complicated by the present invention.

The present invention will become more apparent from the followingdescription of the preferred embodiments thereof taken in conjunctionvwith the accompanying drawings, in which;

FIG. 1 is a circuit diagram, with block diagram in part, illustrating aflash device and an EE circuit of a camera in accordance with theinvention;

FIG. 2 is a circuit diagram, schematic in part illustrating anotherembodiment in accordance with the invention;

FIG. 3 is a circuit diagram, with block diagram in part, of a thirdembodiment of the present invention;

FIG. 4 is a graph for explanation of the mode of operation of thepresent invention;

FIG. 5 is a circuit diagram of a fourth embodiment of the presentinvention; I

FIG. 6 is a circuit diagram of a fifth embodiment of the presentinvention;

FIG. 7 is a circuit diagram of a sixth embodiment of the presentinvention;

FIG. 8 is a circuit diagram of a still another embodiment of a flashdevice and a camera system having this flash device in accordance withthe invention;

FIG. 9 is a circuit diagram of a still another embodiment in accordancewith the present invention;

FIG. 10 is a circuit diagram of a still another embodiment of theinvention; and

FIG. 11 is a circuit diagram of one example of practical flash deviceand auto-flash mechanism of camera to which is attached the flashdevice. 4

It should be noted that throughout the drawings the same components willbe shown with the same reference numerals or characters. I

Referring to FIG. l illustrating a circuit diagram of flash device andan EE circuit in accordance with the present invention, the EB circuit Ecomprises a variable resistor 1, and the variable resistor 1 isconnected in parallel with an ammeter 2 and is adapted to be adjusted inaccordance with the sensitivity of the film and the guide number. Thestop value of a photo lens is automatically set in accordance with theindication by a pointer of ammeter 2 as being well known in the art. Aphotoconductive element 3 such as cadmium sulphide (CdS) is connected inseries to a power source 4.

Reference numeral 5 designates a variable resistor whose resistance isvaried in response to the angle of rotation of a focusing ring; 6, aswitch; and 7 and 7, terminals for connection of the EB circuit with theflash device. A flash device comprises a main capacitor 11, a dischargelamp circuit F including gas discharge lamp 12, a power supply circuit Fincluding a battery, and a control circuit C including a potentiometer10 for dividing a voltage across main capacitor 11 and transistors 8 and9.

Next the mode of operation will be described. In case of daylightphotography, switch 6 is opened and a suitable aperture for a givensubject-brightness is determined by the EB circuit. In the case of aflash exposure with a flash bulb whose guide number is constant, switch6 is closed so as to couple variable resistor 5 to the BE circuit,whereby the auto-flash mechanism is established for flash exposure. Whenthe flash device in accordance of the present invention is coupled tothe camera for flash exposure, switch 6 remains opened while the powerswitch (not shown) of the flash device is closed, whereby main capacitor11 is charged. The energy stored in the capacitor is expressed by CV /2which is proportional to the guide number. Thus, the voltage acrosscapacitor 11 is detected so as to control the auto-flash mechanism,whereby the latter may be actuated by the brightness of the'flash devicewhich is ready to flash. More specifically, a fraction of the voltageacross capacitor 11 is applied by potentiometer from its moving arm tothe base electrode of NPN transistor 9 whose collector is connected tothe base of PNP transistor 8. The emitter and collector of PNPtransistor 8 are connected to auto-flash mechanism or EE circuit Eso.that the deflection of the pointer of meter 2 varies depending uponthe charged voltage across capacitor 11. When the voltage acrosscapacitor 11 is small, the collector current is less so that the pointerof meter 2 deflects through a small angle.

On the other hand, when the voltage across capacitor 11 is high, thepointer deflects through a large angle, indicating the stop-in. Whenpotentiometer 10 is so adjusted that a predetermined guide number may beindicated when the voltage across capacitor 11 reaches a predeterminedvalue, the guide number of the flash devices is varied accordingly.Thus, the deflection of pointer of the meter 2 is also variedaccordingly so that the flash exposure can be made with a suitable oroptimum exposure factor. In order to indicate the fact that the voltagecharged across main capacitor 11 reaches a minimum voltage which canstart flashing of flash lamp 12, a meter on the side of the camera maybe used. In this case, this meter may be so arranged as to be viewed inthe field of the rangeflnder, whereby an operator can continuously andadvantageously carry out flash exposures without leaving his eye fromthe viewfinder, that is, from the subjects to be photographed.

Next, the second embodiment of the present invention will be describedwith reference to FIG. 2. Instead of potentiometer 10 as in the firstembodiment shown in FIG. 1', a bias voltage having the polarity oppositeto that of the power source (not shown) in power circuit P is applied soas to vary in response to a voltage charged across main capacitor 11 inorder to control the current flowing through the EB circuit, that is, tocontrol the deflection of the pointer of the meter 2.

In control circuit C of the second embodiment, a

Zener diode 16 is interconnected for obtaining a constant voltage, andan NPN transistor 17 has its base connected to the emitter of an NPNtransistor 18 whose base is connected to a neon discharge lamp 19. 20designates a bias source, as set forth above. When the voltage acrossmain capacitor 11 of the flash device is less than the minimum voltagefor initiating the flashing of flash lamp 12 (see FIG. 1), neondischarge lamp 19 is not ignited so that both of the transistors'l7 and18 remain in the non-conductive state. A voltage across the outputterminals A and B is substantially equal to that of bias source 20. Whenthe voltage across the main capacitor 11 rises above the minimum voltagefor initiating the flashing of the flash lamp, neon discharge lamp 19 isignited so that both of the transistors 17 and 18 are renderedconductive. Therefore, the polarity at the output terminals A and B arereversed so that the pointer of the meter 2 defects through a certainangle, whereby the operator can recognize the fact that the flash deviceis ready to flash at any moment.

When the voltage across capacitor 11 is further raised, the voltageacross the terminals A and B is also increased accordingly so that theexposure factor for flash exposure may be automatically determined by EBcircuit E.

From the foregoing it is seen that even when the guide number of theflash device is deviated from a reference value due to the voltagecharged across main capacitor 11, the EB circuit may be controlledaccordingly, thereby accomplishing the flash exposure with a suitableexposure factor. Furthermore, the operator can see through theviewfinder the sign representative of the completion of readying theflash device for flashing, thus ensuring proper flash exposure in a veryeffective and simple manner.

Because of the operating range and rise time characteristic of atransistor, the operating range of the flash device is sometimes notsufficient. The embodiments illustrated in FIGS. 3 and 5 contemplateeliminating this defect, thereby providing the flash device which can beactuated in a positive manner even at a lower voltage. Thus, theembodiments of the present invention incorporate therein an improvedtransistorized control circuit.

Referring to FIG. 3, there is shown a direct step-up circuit employingtransistors used as a power supply circuit for the flash device. 11 is amain capacitor, and F, a discharge lamp circuit including a triggercircuit. A controlcircuit C includes a series resistor 23, a neondischarge lamp 24, a transistor 25, diodes 26 and 27 and resistors 28,29 and 30. E is the auto-flash mechanism of the camera.

FIG. 4 is for explanation of the mode of operation of the instantembodiment, illustrating the relation between a voltage across maincapacitor 11 and a current flowing through a load or auto-flashmechanism E. Upon closure of a power switch (not shown) of the flashdevice, main capacitor 11 is charged by the charging current from thepower circuit P.

When the voltage across main capacitor 11 reaches the minimum voltagecapable of initiating the flashing of the discharge lamp in dischargelamp circuit F, neon discharge lamp 24 is ignited so that the currentflows from the base to the emitter of the transistor 25, whereby theload current as shown in FIG. 4 flows through the output circuit.Assuming that only resistor element is interconnected in the basecircuit of the transistor, then the load current is shown by curve c inFIG. 4 and the voltage across the main capacitor 11 becomes C when thepointer of the meter in the load circuit indicates the maximum orcritical value L. However, when diode 26 is interconnected in the basecircuit as shown in FIG. 3, the input voltage to the transistor iscompressed due to the nonlinearity thereof so that the load current isshown by curve d in FIG. 4. Thus, when the meter indicates the maximumor critical value L, the voltage across main capacitor 11 becomes D.This means that the operating range of the BE circuit due to the voltageacross main capacitor 11 is widened. In the instant embodiment, diode 27is interconnected so as to interrupt the input current of the transistoras shown in FIG. 3, so that the circuit may have a high input impedance.Furthermore, biasresistor 30 is employed. Thus, the rise timecharacteristic of the transistor is improved so that the positiveswitching action can be ensured when the neon discharge lamp istriggered.

The fourth embodiment illustrated in FIGS employs a field effecttransistor 32 in the control circuit. When FET 32 is used, it is nolonger required to improve the rise time characteristic of thetransistor. It is just interconnected to diodes 33 and-33' forcompression" of the input voltage. Diodes 34 and 34' are interconnectedfor obtaining a bias voltage for PET 32.

In the instant embodiment, the control range of the auto-flash mechanismor EE circuit due to the voltage across main capacitor 11 may bewidened. The more positive operation can be ensured and the moreeffective design of the flash device becomes possible,

The fifth and sixth embodiments illustrated in FIGS. 6 and 7 are soarranged to automatically determine the optimum exposure factor incooperation with the autoflash mechanism of a camera system having aflash device for flash exposure and more particularly the BE camera. InEE circuit E, a resistor 35 for setting the sensitivity of the film tobe used is interconnected in parallel with ammeter 2 and a resistor 36for setting the range in case of flash exposure is also interconnectedin the circuit. 4 is a battery of the BE circuit and 7 and 7, theterminals for coupling the camera to the flash device. The abovecomponents are arranged in the camera.

In FIG. 6, the control circuit C of the flash device includes diodes 37,37' and 37" connected in parallel with one another, resistors 38, 38 and38" connected in series with diodes 37, 37' and 37" respectively, neondischarge lamps 39, 39 and 39" connected in series to these resistorsrespectively; and resistors 40, 40 and 40" connected in series theretorespectively. 11 designates a main capacitor of the flash device; F, thedischarge lamp circuit; and P, the power supply circuit for flashdevice.

When the power switch (not shown) in the power supply circuit P isclosed, capacitor ll is charged by the current from the power supplycircuit P. When the voltage charged across the main capacitor 11 reachesthe minimum voltage capable of initiating the flashing of any one of thedischarge lamps in the discharge lamp circuit, the resistor 40 is soconnected that the first neon lamp 39 is turned on.

A certain current flows through the diode 37 and the resistor 38 by theswitching action of the neon lamp 39 so that the pointer of the meter 2of the EB circuit deflects through a certain angle. When the shutterrelease button is released under this condition, the exposure is madethrough an aperture which is determined in response to the angle throughwhich the pointer of the meter deflects. Thereafter, when the voltagecharged across the main capacitor 11 reaches a predetermined voltagelevel, the neon lamp 39 is turned on so that the circuit elements, thatis the diode 37' and the resistor 38' are connected to the EB circuit sothat the current flowing through the circuit elements 37 and 38 and thecurrent flowing through the circuit elements 37' and 38' flow throughthe EB circuit. Thus, the pointer of the meter 2 deflects more. When theneon discharge lamp 39" is turned on, all of the currents flowingthrough the branched circuits each consisting of the diode, the resistorand, the neon lamp flow through the BE circuit, whereby the pointer ofthe meter 2 is deflected more and more. a

In order that the neon discharge lamps 39, 39' and 39" are turned onsequentially, the values of the resistors 40, 40 and 40" are suitablyselected. Thus, the voltage charged across main capacitor 11 may bedetected in steps or digitally, whereby the pointer of the meter in theEB circuit is deflected. Since diodes 37, 37' and 37" are connected inthe direction as shown in FIG. 6, the current from battery 4 in the EBcircuit is permitted to flow through the meter.

The sixth embodiment illustrated in FIG. 7 is a variation of the fifthembodiment shown in FIG. 6.

When a resistor 41 is employed as shown in FIG. 7, instead of resistors40, 40 and 40" as in FIG. 6, and diodes 42 and 43 are interconnected asshown in FIG. 7, neon lamps 39, 39 and 39" are also turned onsequentially in response to the rise of the voltage charged across maincapacitor 11 by varying the voltages for triggering the lamps. It shouldbe noted that instead of the neon lamps, thyristors or any othersuitable switching elements can be employed for attaining the samefunction.

The embodiments illustrated in FIGS. 8, 9 and 10 are so arranged todetect the voltage across the main capacitor of the flash device by useof the EB circuit incorporated in the camera, thereby controlling the EBcircuit by the variation in resistance of a photoconductive elementdisposed in opposed relation with a light source whose luminescencevaries, whereby the optimum exposure may be attained automatically inresponse to the angle of deflection of the pointer of the ammeter.

FIG. 8 is a circuit diagram of a camera system having the flash devicein accordance with the present invention. E designates the BE circuit,and a control circuit C includes a light source 48 such as a neondischarge lamp disposed in opposed relation with a photoconductiveelement 47. A main capacitor is designated by 11; a power circuit, by P;and a discharge lamp circuit including a trigger circuit, by F. When thevoltage across the capacitor 11 reaches a minimum voltage which caninitiate the flashing of the discharge lamp, neon lamp 48 is turned onand the light therefrom is intercepted by photoconductive element 47.Thus, it is readily seen that the resistance of photoconductive element47 is varied in response to a voltage across main capacitor 11. Both ofterminals of the photoconductive elements 47 are connected to the EBcircuit in the camera so as to control the current flowing through theBE circuit.

Therefore, the optimum exposure can be accomplished automatically inresponse to the deflection of pointer of the ammeter 2 as in the case ofthe conventional EE camera. In the instant embodiment, the luminescenceof the flash device is detected from a small light source and convertedinto the variation in resistance of the photoconductive element disposedin opposed relation with the light source so that the flash device isnot electrically coupled to the BE circuit in the camera. This latterfeature of the instant embodiment should be particularly noted.

FIG. 9 illustrates the eighth embodiment of the present invention. Edesignates the EB circuit in the camera which comprises ammeter 2,variable resistors 35 and 36 for setting the sensitivity of the film tobe used and setting the range or distance, andbattery 4 of the BEcircuit. lldesignates a main capacitor of the flash device; P, a powercircuit; F, a discharge lamp circuit including a trigger circuit; and Ca control circuit including neon lamp 49, potentiometer 50, NPNtransistor 51 and photo-coupler consisting of miniaturized lamp 52 and aphotoconductive element 53. Main capacitor 11 is charged by the currentfrom the power source of the flash device. When the voltage across maincapacitor 11 reaches the minimum voltage capable of initiating theflashing, neon discharge lamp 49' is turned on and transistor 51 isrendered conductive by the voltage divided by potentiometer 50, wherebylamp 52 is turned on. The light from lamp 52 is intercepted byphotoconductive element 53 disposed in opposed relation therewith sothat the resistance of photoconductor element 53 is varied in responseto a voltage across main capacitor 11.

The circuit is coupled to the BE circuit in the camera as shown so as tocontrol the current flowing therethrough, whereby the optimum exposurecan be attained automatically in response to the deflection of thepointer of the ammeter 2.

FIG. 10 illustrates still another embodiment of the present inventioncomprising power circuit P, discharge lamp circuit F and control circuitC. The control circuit includes a photo-coupler consisting of a group ofneon lamps 55, 55' and 55" connected in parallel and photoconductiveelement 56 in opposed relation therewith for intercepting the lightemanating therefrom, and resistors 54, 54' and 54" connected in seriesto the neon lamps respectively as shown. The voltage across capacitor 11may be detected in steps by neon discharge lamps 55, 55 and 55" whoselight is in turn detected by photoconductive element 56, whereby thevoltage'across capacitor 11 may be detected as the variation inresistance of photoconductive element 56. Thus, the EB circuit in thecamera may be controlled so that the deflection of the pointer ofammeter 2 may be varied in steps.

In the embodiments described hereinabove with reference to FIGS. 8, 9and 10 the EB circuit can be controlled by the voltage across maincapacitor 11 through photo-coupler means consisting of a neon dischargelamp or lamps and a photoconductive element disposed in opposed relationtherewith. Thus, the BE circuit is not electrically coupled to the flashdevice so that the design and use of the flash device in accordance withthe present invention are much facilitated. Furthermore, the BE functioncan be attained by a simple circuit even when flash exposure is made.

Next referring to FIG. 1 l, a highly detailed circuit in accordance withthe present invention will be described for better understanding of thepresent invention.

Reference numeral refers to a transistor for oscillation andinterconnected to primary 64 and the feedback winding 63 of atransformer 78; 62, the secondary of transformer 78 is connected throughrectifier element 61 to main discharge capacitor 1 l; and F, a dischargecircuit including trigger coil 57, resistor 58 for charging triggercapacitor 59, and flash lamp l2. Discharge circuit F is coupled to flashsynchronization terminal 77 of the EB circuit E in the camera. A controlcircuit includes variable resistor 60 connected in parallel with maincapacitor 11, neon discharge lamp 24, diodes 70, 71 and 74 andtransistor 25. The control circuit further includes emitter resistor 68of transistor 25, variable resistor 69 for correcting the voltage dropacross emitter resistor 68, diode 73 for obtaining a constant voltageand bias resistor 72 for applying a predetermined voltage across diodes73 and 74. Diodes 70, 71 and 74 serve to compress the variation involtage across the main capacitor 1 1 and to compensate for the risetime of the voltage across the base and emitter of transistor 25.

Switch 75 is interlocked with power switch 67 of the flash device insuch a manner that when power source 66 of the flash device is turnedoff, the EB circuit in the camera is disconnected from the control ofthe flash device. Auto-flash mechanism E in the camera includes ammeter2 cooperable with an aperture, photoconductive element 3, variableresistor 35 connected in parallel with ammeter 2 for setting thesensitivity of the film and power source 4. Variable resistor 36 isinterlocked with a focusing ring. Switch 76 serves to safeguard againstelectric shock and is opened when the flash device is attached to thecamera and closed when detached, so as to short-circuit the high-voltageterminal for flash syncronization to a lower voltage level.

Reference numeral 80 designates a diode for protecting diodes 73 and 74and transistor 25 from the-reverse voltage.

The mode of operation is as follows. First the flash device is attachedto the camera and power switch 67 is turned on so that switch 75coacting with power switch 67 is closed, whereby the voltage acrossdiodes 73 and 74 (for example 1.3V) is applied in the direction so as tocancel voltage 4 (for example, the mercury battery with 1.3V) of the BEcircuit. In this case, it should be noted that the pointer of ammeter 2is not deflected.

As soon as switch 67 is closed, the DC-DC converter consisting ofcircuit elements 61, 62, 63, 64 and 65 is energized so that the highvoltage induced across secondary 62 is applied through rectifier 61 tomain discharge capacitor 11, whereby the latter is charged. When maincapacitor 11 is charged to a predetermined level for initiating theflashing, neon discharge lamp 24 is rendered conductive so thattransistor 25 is also rendered conductive in a switch-like fashion.Therefore, a voltage drop (for example, 0.8V) occurs across emitterresistor 68 so that the voltage applied to the EB circuit in the reversedirection drops from 1.3V to 0.5V, whereby the pointer of the ammeterindicates a guide number, in jumping fashion, corresponding to thevoltage across capacitor 1 1.

As the voltage across main capacitor 11 is increased, the voltage dropacross emitter resistor 68 is increased,

the voltage applied in the reverse direction to the EB circuit isreduced and then the current flow through ammeter 2 increases. Whenthe-voltage across main capacitor 11 reaches the peak voltage, thevoltage drop across emitter resistor 68 becomes approximately equal tothat across diodes 73 and 74 (for example, 1.3V) so that the reversevoltage applied to the BE circuit becomes zero.

Ammeter 2 indicates this accordingly.

Upon focusing adjustment, variable resistor 36 cooperating therewithvaries its resistance so as to control the current flowing through theammeter. For example, if the distance between the flash device and asubject is relatively small, the resistance of variable resistor 36 islow so that much current flows through ammeter 2 whereby the diaphragmis closed. On the other hand, when the distance is relatively large,less current flows through the ammete'r so that the diaphragm is openedaccordingly. That is, the nearer the subject, the more the diaphragm isclosed. Upon depression of the shutter button, flash synchronizationswitch 77 is closed in synchronism with the actuation of the shutterblades or the like and the trigger pulse is induced across the secondaryof trigger coil 78 for triggering discharge lamp 12. When discharge lamp12 is triggered the charge stored in main discharge capacitor 11 isdischarged through the lamp, thereby flashing the light for exposure.Neon lamp 24 is rendered non-conductive and the voltage drop acrossemitter resistor 68 becomes zero so that the voltage for cancelling thepower source voltage is applied to the BE circuit and the pointer of theammeter will not deflect at all. Thus, the next flash exposure cycle isready to start.

Having thus described the invention; it will be apparent to thoseskilled in the art that various modifications can be made within thespirit and scope of the present invention. For example, in theconventional EE camera, the shutter button is generally locked when thepointer of the ammeter does not deflect or does deflect beyond apredetermined value. This warning system may be alsoused for indicationof the operating range of the flash device. When switch 67 is opened,switch 75'cooperating therewith is also opened so that the camera may beunder the control of the BE circuit even when the flash device isattached thereto.

What is claimed is:

1'. A flash exposure control system for a camera comprising:

a capacitor; a power supply circuit coupled to said capacitor forcharging said capacitor; a discharge circuit including a discharge lampcoupled to said capacitor; and exposure meter circuit including anexposure meter; and control circuit means operatively coupled betweensaid capacitor and said exposure meter circuit for producing an outputcontrol signal for controlling the deflection of said exposure meter inresponse to variations in the charge stored in said capacitor.

2. A flash exposure control system as set forth in claim 1, wherein saidcontrol circuit means comprises at least one switching element coupledto said capacitor and responsive to a predetermined voltage across saidcapacitor to produce said output control signal.-

3. A flash exposure control system as set forth in claim 2, wherein saidswitching element comprises a neon discharge lamp which conducts whenthe voltage across said capacitor reaches a predetermined level.

4. A flash exposure control system as set forth in claim 2, wherein saidcircuit control means further comprises: photo-coupler means includinglight emissive means coupled to said switching element, and lightresponsive means coupled to said exposure meter, said photo-couplerbecoming energized in response to the energization of said switchingelement for producing said output control signal.

5. A flash exposure control system as set forth in claim 1, wherein saidcontrol circuit means comprises: a plurality of switching elements, eachconnected in parallel with said capacitor for respectively switching toa conductive state in response to mutually different predeterminedcharge levels of said capacitor; and a plurality of signal conductingmeans, coupled one each to said plurality of switching elements and tosaid exposure meter, and each becoming energized in response to the saidswitching to a conductive state of the respective switch element coupledthereto.

6. A flash exposure control system as set forth in claim 1, wherein saidcontrol circuit means includes a detecting circuit for detecting thevoltage across said capacitor, and a voltage source connected to saiddetecting circuit in an opposed-polarity relationship with respect tothe polarity of said voltage across said capacitor.

7. A flash exposure control system as set forth in claim 1 and furthercomprising:

constant voltage means for providing a constant voltage referenceportion of said output control signal.

8. A flash exposure control system as set forth in claim 1, wherein saidcontrol circuit means comprises a photo-coupler including: at least onelight emissive means coupled to said capacitor; and light responsivemeans coupled to said exposure meter for producing said output controlsignal.

9. A flash exposure control system as set forth in claim 1, wherein saidcontrol circuit means comprises a photo-coupler including: a pluralityof light emissive means, and a plurality of resistors, wherein eachvlight emissive means is series connected with a resistor across saidcapacitor; and a plurality of light responsive means optically coupledrespectively to said plurality of light emissive means, and eachcoupledto said exposure meter for producing said output control signal.

It). A flash exposure control system for a camera as set forth in claim1, in which said control circuit means includes diode circuit means forproviding a non-linear output control signal for increasing the responserange of said exposure meter with respect to said variations incharge-stored in said capacitor.

11. A flash exposure control system for a camera as set forth in claim1, in which said control circuit means comprises a detecting circuit fordetecting the voltage across said capacitor, and semiconductor circuitmeans coupled between said detecting circuit and said exposure meter forproducing said output control signal in response to variations of thesaid voltage detected by said detecting circuit.

12. A flash exposure control system for a camera as set forth in claim1], in which said semiconductor circuit means includes diode circuitmeans for providing a non-linear output control signal for increasingthe tion of said meter to indicate a non-optimum value when said chargeon said capacitor is below a predetermined level.

14. A flash exposure control system for a camera as set forth in claim13, in which said switching means includes a plurality of voltagesensitive switching devices to control said deflection in stepscorresponding to a plurality of predetermined charge levels on saidcapacitor.

15. A flash exposure control system for a camera, as set forth in claim1, in which said control circuit means includes potentiometer meanscoupled to said capacitor for providing manual adjustments to saidoutput control signal.

UNITED STATES PATENT OFFKCE "Patent No. 3,714 8 72" bated February 6,1973 Inventor (s) YUKIQ'MASHIMO, SEIICHIRO MI'ZUI, and YOSHIYUKITAKISHIMA.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby co rrecged as shown below:

Column 2, line 47, after "of" insert a-';

' Column 3, line 47, change "leaving" to -re movi'ng- Colurim 4',- 'line1, after "both" delete "of the";-

Column 7, lines 28-29", Pphotoconductot" should read v -photoconductive? Column 9, line 54, change and" to '-an--.

Signed and sealed thief-10th day of July 1973.

' (SEAL) I Attestz EDWARD M.FLETCHER,JR. v Rene Tegtmeyer A'eEesti-ngOfficer y I Acting Commissioner of Patents l "I 0-217- UNITED STATESPATENT OFFICE.

- CERTIFICATE OF CORRECTION Patent No .j3 ,7l4 872 V I February 6', 1973Inventor (s) YUKIQ MASHIMO, SEI ICHIRO MI'ZUI, and YOSHIYUKI TAKISHIMA.A It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby co rrectged as shown below:

Column 2, line 47, after "of" insert a--";

Column 3, line 47, change "leaving" to -remov i'ng-;

Column 4, line 1, after "both" delete "of the" Column 7, lines 28-29"photoconducto'r" should read ;.photoconduCtive- Column 9 line 54;change "and" to '-an-.

. Signed and sealed this" 10th day of July 1973.

(SEAL) Attest:

EDWARD.M.FLETCHER,JR. V Rene Tegtmeyer Afutestlng Officer I ActingCommissioner of Patents

1. A flash exposure control system for a camera comprising: a capacitor;a power supply circuit coupled to said capacitor for charging saidcapacitor; a discharge circuit including a discharge lamp coupled tosaid capacitor; and exposure meter circuit including an exposure meter;and control circuit means operatively coupled between said capacitor andsaid exposure meter circuit for producing an output control signal forcontrolling the deflection of said exposure meter in response tovariations in the charge stored in said capacitor.
 1. A flash exposurecontrol system for a camera comprising: a capacitor; a power supplycircuit coupled to said capacitor for charging said capacitor; adischarge circuit including a discharge lamp coupled to said capacitor;and exposure meter circuit including an exposure meter; and controlcircuit means operatively coupled between said capacitor and saidexposure meter circuit for producing an output control signal forcontrolling the deflection of said exposure meter in response tovariations in the charge stored in said capacitor.
 2. A flash exposurecontrol system as set forth in claim 1, wherein said control circuitmeans comprises at least one switching element coupled to said capacitorand responsive to a predetermined voltage across said capacitor toproduce said output control signal.
 3. A flash exposure control systemas set forth in claim 2, wherein said switching element comprises a neondischarge lamp which Conducts when the voltage across said capacitorreaches a predetermined level.
 4. A flash exposure control system as setforth in claim 2, wherein said circuit control means further comprises:photo-coupler means including light emissive means coupled to saidswitching element, and light responsive means coupled to said exposuremeter, said photo-coupler becoming energized in response to theenergization of said switching element for producing said output controlsignal.
 5. A flash exposure control system as set forth in claim 1,wherein said control circuit means comprises: a plurality of switchingelements, each connected in parallel with said capacitor forrespectively switching to a conductive state in response to mutuallydifferent predetermined charge levels of said capacitor; and a pluralityof signal conducting means, coupled one each to said plurality ofswitching elements and to said exposure meter, and each becomingenergized in response to the said switching to a conductive state of therespective switch element coupled thereto.
 6. A flash exposure controlsystem as set forth in claim 1, wherein said control circuit meansincludes a detecting circuit for detecting the voltage across saidcapacitor, and a voltage source connected to said detecting circuit inan opposed-polarity relationship with respect to the polarity of saidvoltage across said capacitor.
 7. A flash exposure control system as setforth in claim 1 and further comprising: constant voltage means forproviding a constant voltage reference portion of said output controlsignal.
 8. A flash exposure control system as set forth in claim 1,wherein said control circuit means comprises a photo-coupler including:at least one light emissive means coupled to said capacitor; and lightresponsive means coupled to said exposure meter for producing saidoutput control signal.
 9. A flash exposure control system as set forthin claim 1, wherein said control circuit means comprises a photo-couplerincluding: a plurality of light emissive means, and a plurality ofresistors, wherein each light emissive means is series connected with aresistor across said capacitor; and a plurality of light responsivemeans optically coupled respectively to said plurality of light emissivemeans, and each coupled to said exposure meter for producing said outputcontrol signal.
 10. A flash exposure control system for a camera as setforth in claim 1, in which said control circuit means includes diodecircuit means for providing a non-linear output control signal forincreasing the response range of said exposure meter with respect tosaid variations in charge stored in said capacitor.
 11. A flash exposurecontrol system for a camera as set forth in claim 1, in which saidcontrol circuit means comprises a detecting circuit for detecting thevoltage across said capacitor, and semiconductor circuit means coupledbetween said detecting circuit and said exposure meter for producingsaid output control signal in response to variations of the said voltagedetected by said detecting circuit.
 12. A flash exposure control systemfor a camera as set forth in claim 11, in which said semiconductorcircuit means includes diode circuit means for providing a non-linearoutput control signal for increasing the response range of said exposuremeter with respect to said voltage variations across said capacitor. 13.A flash exposure control system for a camera as set forth in claim 1, inwhich said control circuit means includes switching means for applyingsaid output control signal to said exposure meter to control saiddeflection of said meter to indicate a non-optimum value when saidcharge on said capacitor is below a predetermined level.
 14. A flashexposure control system for a camera as set forth in claim 13, in whichsaid switching means includes a plurality of voltage sensitive switchingdevices to control said deflection in steps corresponding to a pluralityof predetermined charge levels on said Capacitor.